Methanol is a major chemical raw material used to make a variety of products, including acetic acid, formaldehyde, and methyl tertiary butyl ether. Worldwide demand is expected to significantly increase as new applications for the use of methanol become commercialized. Such new applications include the conversion of methanol to gas, such as the Mobil MTG process; the conversion of methanol to olefins, gasoline and distillate, such as the Mobil MOGD process; and the conversion of methanol to olefins, such as the MTO process.
For example, in U.S. Pat. Nos. 6,444,712 B1 and 6,486,219 B1 to Janda, a method for producing olefins from methanol, by way of using natural gas to make the methanol, is described. The method includes converting the methane component of the natural gas to synthesis gas (syngas) using a steam reformer and a partial oxidation reformer. The syngas from each reformer is combined and sent to a methanol synthesis reactor. The combined syngas stream to the methanol synthesis reactor desirably has a syngas number of from about 1.4 to 2.6. The methanol product is then used as a feed in a methanol to olefin production process.
Much of the methanol made today is made under high purity specifications. Grade A and grade AA methanol are commonly produced. U.S. Pat. No. 4,592,806 to Ilgner discloses a process for producing the grade AA methanol. The grade AA methanol has a maximum ethanol content of 10 ppm and is produced using a distillation column, and distilling fusel oil at a reflux ratio of at least 5:1.
The use of crude, or substantially unrefined, methanol has been suggested for use in making olefins. In U.S. Pat. No. 5,714,662 to Vora, there is disclosed an integrated process for producing light olefins from a hydrocarbon gas stream by combining reforming, methanol production, and methanol conversion. The methanol produced is a crude methanol, which is essentially unrefined and comprises methanol, light ends, and heavier alcohols. The crude methanol is passed directly to an oxygenate conversion zone to produce light olefins.
As the production of methanol continues to increase, and the new commercial uses of methanol also continue to increase, it would be advantageous to produce variable quality methanol streams, which have particular advantages for specific end uses, and which do not have to meet the stringent requirements of Grades AA and A methanol. It would also be beneficial to provide various processes for which the methanol streams would be of particular benefit.